X-chain - consolidate tx creation in unit tests #3666

Job	Run time
e2e	10m 40s
Fuzz	12m 59s
e2e_existing_network	3m 29s
Unit (macos-12)	11m 50s
Upgrade	3m 16s
Unit (ubuntu-20.04)	6m 48s
Unit (ubuntu-22.04)	6m 47s
Protobuf Lint	8s
Unit (windows-2022)	13m 48s
Unit (self-hosted, linux, ARM64, focal)	1m 24s
Unit (self-hosted, linux, ARM64, jammy)	1m 24s
Up-to-date protobuf	27s
Up-to-date mocks	2m 24s
Up-to-date go.mod and go.sum	17s
Lint	2m 54s
	1h 18m 35s

Provide feedback